+1 on brino's BBQ grill approach. I used that method when I repaired a cracked coal stove chimney manifold a few years ago. I was pre and post heating with a torch and stick welding it, just like others have said I used short welds and peened it well but it kept cracking. I had welded cast successfully before without too much trouble but that part was real nightmare. As a last attempt, I tossed a bag of charcoal in the Webber grill, fired it up, got the part pre heated and welded all the cracks, put the lid on, closed the air vents and let die out. Part cooled without cracking and is still in use. I don't remember the rod I used but it was bought from McMaster Carr, recommend for cast iron.